The present invention relates to the transmission of optical signals, in particular optical signals having sub-signals of non-uniform bandwidth.
Optical transmission equipment in current use today supports a number of sub-signals, each of which has a known wavelength and a fixed bandwidth. For example, the transmission equipment may support 100 sub-signals, each sub-signal being OC-192 based. The numberxe2x80x9c100xe2x80x9d of sub-signals mentioned here is an arbitrary number as it is technically possible to support more, closely spaced sub-signals of lower bandwidth, or less, widely spaced sub-signals of higher bandwidth.
In instances when a data signal must be transported by a sub-signal, the bandwidth of the data signal is usually significantly lower than the bandwidth of the sub-signal. In this instance, it is known to use a multiplexing mechanism such as a Time Division Multiplexing (TDM) mechanism to carry the data signal over the higher bandwidth pipe constituted by the sub-signal.
This approach presents two distinct drawbacks. First, the necessity to use a multiplexing mechanism makes the optical transmission system complex. Second, when the sub-signal is subdivided, the various parts that result from the division are all usable independently with the exception that such use is restricted over the entire length of the sub-signal path. For example, a second data signal can be multiplexed with the first data signal and both signals transported over the sub-signal at the condition that the first and second data signals follow exactly the same path through the optical transmission system. In practice, this is not always the case since the second data signal may follow a different route than the first data signal. Accordingly, the current approach lacks flexibility.
Against this background, it clearly appears that a need exists in the industry to develop a method and a system for optical transmission that resolves, or at least alleviates, some of the drawbacks associated with the current technology.
In a first broad aspect, the invention provides an optical medium containing a transport signal that has a plurality of sub-signals, each sub-signal being characterized by a known wavelength of light and a known bandwidth, the bandwidth of the sub-signals being non-uniform, in other words, at least one of the sub-signals has a bandwidth that is different from the bandwidth of another sub-signal.
This approach makes possible the use of sub-signals that are tailored, at least to some degree, to the bandwidth of the- data signals to be transported. As a consequence, the necessity to implement a multiplexing mechanism over one or more sub-signals is reduced, perhaps even eliminated.
Under a specific and non-limiting example of implementation, the invention provides an optical transmission system that comprises a transmitter element, an optical transmission medium such as an optical fiber and a receiver element. In addition to using sub-signals of non-uniform bandwidth, the sub-signals are also spaced in the optical frequency domain in a non-uniform manner. Under this example of implementation, the sub-signal spacing is related to the bandwidth of the sub-signals. For instance, sub-signals of relatively low bandwidth are spaced closer than signals of relatively high bandwidth. One advantage of this exemplary embodiment is the ability to increase the number of sub-signals in the transport signal. It follows that the number of different paths that can be established in the optical transmission system can also be increased in the interest of providing more flexible transport solutions.
Under a second broad aspect, the invention provides a transmitter element having an output for connection to an optical transmission medium, the transmitter element being operative to generate at the output an optical transport signal that has a plurality of sub-signals. Each sub-signal is characterized by a known wavelength of light and a known bandwidth where the bandwidth of the sub-signals is non-uniform.
Under a third broad aspect, the invention provides a receiver element having an input and an output, the input being suitable for connection to an optical transmission medium conveying an optical transport signal that has a plurality of sub-signals. Each sub-signal is characterized by a known wavelength of light and a known bandwidth where the bandwidth of the sub-signals being non-uniform. The receiver element is operative to generate at the output an electrical signal in dependence of at least one of the sub-signals in the optical transmission medium.